Such a process is known from Tetrahedron Lett. 34, 1181-1184 (1993), which describes the oxidation of monosaccharides wherein the non-primary hydroxyl groups are partly protected, using sodium hypochlorite, potassium bromide and TEMPO in a two-phase solvent system (dichloromethane and water) to produce the corresponding uronic acid. WO 95/07303 describes a process for oxidizing carbohydrates with hypochlorite and TEMPO, using a pH of 9-13 in an aqueous median. The oxidation of carboxymethyl and hydroxyethyl derivatives of starch and cellulose and other starch ethers with TEMPO is described in WO 96/38484.
These prior art oxidations have the advantage of being selective, in that oxidation of primary alcohol groups is strongly favored over oxidation of secondary alcohol groups. However, the known processes use hypochlorite as the actual oxidizing agent and thus produce chloride and some chlorinated byproducts: for complete oxidation of primary alcohols to carboxylic acids, two molar equivalents of hypochlorite are used and two molar equivalents of chloride are produced. WO 99/57158 describes the oxidation of carbohydrates using TEMPO and peracetic acid in the presence of bromine.
Recently, Kochkar et el. (J. Catalysis 194, 343-351 (2000)) described the TEMPO-mediated oxidation of α-methyl-D-glucoside (α-MDG), 1,2-propanediol, saccharose and starch with ammonium peroxodisulfate in the presence of a supported sliver catalyst in water at pH 9.5 at 25° C. The oxidation of α-MDG and propanediol was successful (78% conversion and 99% selectivity for oxidation of primary hydroxyl group for α-MDG, 90% conversion and 75% selectivity for propanediol), but the oxidation of saccharose was mediocre (20% conversion) and oxidation of starch was unsuccessful (less than 1% conversion). In the absence of the silver catalyst, the TEMPO oxidation of α-MDG with peroxodisulfate was poor (9% conversion), while replacing peroxodisulfate by Oxone® (2KHSO5.KHSO4.K2SO4) in the presence of silver resulted in only 6% conversion. Thus the teaching of this prior art is that the utility of persulfates for oxidizing primary alcohols is restricted to small substrate molecules and practically to the use of ammonium peroxodisulfate, and that the assistance of a silver catalyst is mandatory. The oxidation of benzyl alcohol and other alcohols with TEMPO and Oxone® in organic solvent to produce aldehydes end ketones was described by Bolm et al. (Org. Lett 2. 1173-1175 (2000)).